Voltage balance circuit, voltage detective circuit, voltage balancing method, and voltage detecting method

ABSTRACT

When a control section ( 39 ) turns on a switch ( 31, 33, 35 ), a capacitor ( 37 ) is connected to a secondary battery (B 1 ) in parallel. Accordingly, voltage between both ends of each capacitor ( 37, 38 ) reaches voltage between both polarities of each secondary battery (B 1 , B 2 ). Thereafter, when the control section ( 39 ) turns off the switch ( 31, 33, 35 ) and turns on a switch ( 32, 34, 36 ), each capacitor ( 37, 38 ) is connected to the secondary battery (B 2 , B 3 ) in parallel. The capacitor ( 37, 38 ) is charged/discharged to balance voltage between both polarities of the secondary battery (B 1  to B 3 ).

TECHNICAL FIELD

The present invention relates to a voltage balance circuit that balancesvoltage between both polarities of each of multiple secondary batteriesconnected to one another in series or a charging voltage of each ofmultiple capacitors connected to one another in series, voltagedetection circuit that detects a charging voltage of each secondarybattery or each capacitor, voltage balance method, and voltage detectionmethod.

BACKGROUND ART

When charging and discharging are repeated many times, the multiplesecondary batteries connected to one another in series cause unbalancein charging voltages of the secondary batteries. Namely, a phenomenonoccurs where charging voltages of the respective secondary batteries arenot equal to each other. When the charging voltages of the respectivesecondary batteries become unequal extremely, there exist secondarybatteries that are sufficiently charged with high voltage and secondarybatteries that are short of charging because of low charging voltages.When the whole multiple series-connected secondary batteries are chargedagain in order to charge the insufficiently charged secondary batteries,the sufficiently charged secondary batteries are overcharged. When thesecondary batteries are overcharged, the life of the barriers becomesshort. Moreover, the insufficiently charged secondary batteries aredischarged, the insufficiently charged secondary batteries areoverdischarged. In the case of overdischarging, discharging cannot beperformed any more. Accordingly, when voltage unbalance occurs, not onlythe entire capacity reduces but also an influence is exerted upon thelife of the batteries, so that the ability cannot be satisfactorilyexerted as a whole.

In order to prevent such voltage unbalance, a voltage detection circuitthat monitors voltage of the secondary battery and a discharge circuitthat discharges the secondary battery based on the monitoring resultwere provided for each secondary battery and there was need to provide avoltage balance circuit shown in FIG. 9.

However, the conventional voltage balance circuit has the followingproblems.

FIG. 9 is a circuit diagram of a voltage balance circuit of theconventional secondary battery.

A voltage balance circuit 10 is one that balances charging voltages ofthree secondary batteries B1, B2, and B3 connected to one another inseries. The voltage balance circuit 10 includes three Zener diodes 11,12, and 13. A cathode of the Zener diode 11 is connected to a positivepolarity of the secondary battery B1. An anode of the Zener diode 11 isconnected to a connecting node N1 between the negative polarity of thesecondary battery B1 and the positive polarity of the secondary batteryB2. A cathode of the Zener diode 12 is connected to the connecting nodeN1. An anode of the Zener diode 12 is connected to a connecting node N2between the negative polarity of the secondary battery B2 and thepositive polarity of the secondary battery B3. A cathode of the Zenerdiode 13 is connected to the connecting node N2. An anode of the Zenerdiode 13 is connected to the negative polarity of the secondary batteryB3.

When the voltage of the corresponding secondary battery B1 exceeds ayield point of the Zener diode 11, current flows into the Zener diode 11and the secondary battery B1 is discharged. When the voltage of thecorresponding secondary battery B1 does not exceed the yield point ofthe Zener diode 11, no current flows and the secondary battery B1 ischarged. The same can be applied to the respective Zener diodes 12 and13. Namely, when the voltages of the corresponding secondary batteriesB2 and B3 are higher than the yield point of the Zener diode 11, currentflows into the respective Zener diodes 12 and 13 and the secondarybatteries B2 and B3 discharge. When they do not exceed the yield point,no current flows into the respective Zener diodes 12 and 13 and thesecondary batteries B2 and B3 are charged. Accordingly, the chargingvoltages of the secondary batteries B1 to B3 are balanced.

While, in the case of balancing the voltages of the respectivecapacitors connected to one another in series, a voltage detectioncircuit that monitors voltage of the capacitor and a discharge circuitthat discharges based on the monitoring result are provided for eachcapacitor. Moreover, there was need to provide a voltage balance circuitas illustrated in next FIG. 10.

A voltage balance circuit 20 is one that balances charging voltages ofthree capacitors C1, C2, and C3 connected to one another in series. Thevoltage balance circuit 20 includes three resistors 21, 22, and 23connected in parallel to the capacitors C1 to C3 respectively. Theresistance values of the resistors 21 to 23 are equal to each other.Voltages divided by the resistors 21 to 23 are applied to connectingnodes of the capacitors C1 to C3. Accordingly, charging voltages of thecapacitors C1 to C3 are balanced.

In the conventional voltage balance circuit 10 of FIG. 9, current flowsinto the respective Zener diodes 11 to 13 to prevent the respectivesecondary batteries B1 to B3 from being overcharged. However, whencurrent flows into three Zener diodes 11 to 13 simultaneously, loss isgenerated by the current to reduce efficiency. Moreover, since thecharging voltages of the secondary batteries B1 to B3 are decided bybreakdown voltage of the respective Zener diodes 11 to 13, there was acase in which the charging voltage varied depending on the accuracy ofthe Zener diodes 11 to 13.

While, in the voltage balance circuit 20 of FIG. 10, since constantcurrent flows into the resistors 21 to 23, loss is generated.

Moreover, when the voltage detection circuit, which detects the chargingvoltage, is provided for each of the secondary batteries B1 to B3 oreach of the capacitors C1 to C3, the circuit scale is increased.

DISCLOSURE OF INVENTION

An object to the present invention is to provide a voltage balancecircuit that is capable of reducing loss and voltage balance method.

Moreover, an object of the present invention is to simplify theconfiguration of a voltage detection circuit that detects voltagesbetween both polarities of the respective storage circuits such assecondary batteries and capacitors that are connected to one another inseries.

In order to attain the above object, a voltage balance circuit accordingto a first aspect of the present invention is a voltage balance circuitthat balances voltage between both polarities of each storage circuit ofa plurality of storage circuits (B1, B2, B3) connected to one another inseries, comprising a capacitor (37, 38), a first connecting section (31,33, 35) that connects the capacitor in parallel to a storage circuitselected from the plurality of storage circuits (B1, B2, B3) connectedto one another in series to charge/discharge the capacitor (37, 38) fromthe selected storage circuit (B1, B2, B3), and a second connectingsection (32, 34, 36) that connects the charged/discharged capacitor (37,38) in parallel to another selected storage circuit (B1, B2, B3)different from the selected storage circuit (B1, B2, B3) tocharge/discharge the another selected capacitor (B1, B2, B3) from thecharged/discharged capacitor (37, 38).

By the adoption of such a structure, the capacitor is connected to theselected storage circuit in parallel to be charged by a charging voltageof the selected storage circuit. By connecting the capacitor to anotherselected storage circuit in parallel, energy transfer from the capacitorto the storage circuit is performed. Accordingly, charging voltages ofthe selected storage circuit and another selected storage circuit arebalanced. In addition, the voltage balance circuit may comprise acontrol section (39) that repeats processing that connects the selectedstorage circuit (B1, B2, B3) to the capacitor (37, 38) in parallel andprocessing that connects the capacitor (37, 38) to the another selectedstorage circuit (B1, B2, B3).

Moreover, each storage circuit of the plurality of storage circuitsconnected to one another in series may include one or multiple secondarybatteries (B1, B2, B3).

Furthermore, each storage circuit of the plurality of storage circuitsconnected to one another in series may include one or multiple secondarycapacitors (C1, C2, C3).

Moreover, the first connecting section and the second connecting sectionmay include a first switch (31, 33, 35) and a second switch (32, 34, 36)that are connected to each other in series between one electrode of theeach storage circuit (B1, B2, B3) and the other electrode, and aconnecting node between the first switch (31, 33, 35) and the secondswitch (32, 34, 36), that are connected to each other in series betweenone electrode of the each storage circuit (B1, B2, B3) and the otherelectrode, may be connected by the capacitor (37, 38).

Furthermore, a voltage detection circuit according to a second aspect ofthe present invention is a voltage detection circuit that detects avoltage between both polarities of each storage circuit of a pluralityof storage circuits (B1, B2, B3) connected to one another in series,comprising a first capacitor (67, 68, 69), a second capacitor (72), acharging section (62, 64, 66, 71) that selects one storage circuit (B1,B2, B3) from the plurality of storage circuits (B1, B2, B3) to chargethe first capacitor (67, 68, 69) by voltage of one electrode of theselected storage circuit (B1, B2, B3), a voltage applying section (61,63, 65, 70) that connects the first capacitor (67, 68, 69) to the secondcapacitor (72) in series to apply voltage of the other electrode of theselected storage circuit (B1, B2, B3) to the first capacitor (67, 68,69) and the second capacitor (72) connected to each other in series, anda pair of measuring terminals connected to both ends of the secondcapacitor (72) to detect voltage between both polarities of the selectedstorage circuit (B1, B2, B3).

By the adoption of such a structure, for example, a negative voltage ofthe selected storage circuit is charged to the first capacitor by thecharging section. In the voltage applying section, a difference voltagebetween the positive voltage of the selected storage circuit and thenegative voltage charged to the first capacitor is applied to the secondcapacitor. Namely, the second capacitor is charged by voltage betweenboth polarities of the selected storage circuit.

In addition, the voltage detection circuit can comprise a controlsection (39) that repeats processing that charges the first capacitor(67, 68, 69) in connection with the selected storage circuit (B1 B2, B3)and processing that applies voltage of the other electrode of theselected storage circuit (B1, B2, B3) to the first capacitor (67, 68,69) and the second capacitor (72) connected to each other in series.

Moreover, the charging section (62, 64, 66, 71) may include a pluralityof first switches (62, 64, 66) each having one end connected to oneelectrode of the each storage circuits (B1, B2, B3) and the other endconnected to one electrode of the each first capacitors (67, 68, 69), acharging switch (71) having one end connected to the other electrode ofthe plurality of first capacitors (67, 68, 69) in common and the otherend connected to a node that sets a reference electric potential, and acontrol section (39) that turns on the first switch (62, 64, 66) havingone end connected to the selected storage circuit (B1, B2, B3) and thecharging switch (71).

Furthermore, one electrode of the second capacitor (72) may be connectedto the other end of the charging switch (71), and the voltage applyingsection (61, 63, 65, 70) may include a plurality of second switches (61,63, 65) each having one end connected to the other electrode of the eachstorage circuit (B1, B2, B3) and the other end connected to oneelectrode of the each first capacitor (67, 68, 69); a voltage applyingswitch (70) having one end connected to the other electrode of theplurality of first capacitors (67, 68, 69) and the other end connectedto the other electrode of the second capacitor (72), and a controlsection (39) that turns off the plurality of first switches (62, 64, 66)and the charging switch (71) and turns on the second switch (61, 63, 65)having one end connected to the selected storage circuit (B1, B2, B3)and the voltage applying switch (70) when voltage of the other electrodeof the selected storage circuit (B1, B2, B3) is applied to the firstcapacitor (67, 68, 69) and the second capacitor (72) connected to eachother in series.

Furthermore, the each storage circuit may include one or multiplesecondary batteries (B1, B2, B3).

Moreover, the each storage circuit may include one or multiplecapacitors (C1, C2, C3).

Furthermore, a voltage detection circuit according to a third aspect ofthe present invention is a voltage detection circuit that detectsvoltage between both polarities of each storage circuit of a pluralityof storage circuits (B1, B2, B3) connected to one another in series,comprising a terminal voltage detecting section (62, 64, 66) thatselects one storage circuit (B1, B2, B3) from the plurality of storagecircuits (B1, B2, B3) connected to one another in series to detectvoltage of one electrode of the selected storage circuit, a pair ofmeasuring terminals (both ends of 71) capable of measuring voltage, anda voltage detecting section (67 to 69, 71) that detects voltage of theother electrode of the selected storage circuit (B1, B2, B3) to show adifferential voltage between the voltage of the other electrode and thevoltage detected by the terminal voltage detecting section (62, 64, 66)to the pair of measuring terminals (both ends of 71) as voltage betweenboth polarities of the selected storage circuit (B1, B2, B3).

By the adoption of such a structure, for example, a negative voltage ofthe selected storage circuit is detected by the terminal voltagedetecting section. A positive voltage of the selected storage circuit isdetected by the voltage detecting section, and a differential voltagecorresponding to the voltage between both polarities of the selectedstorage circuit is detected from the voltage detected by the terminalvoltage detecting section and provided to the pair of measuringterminals. Namely, when the electric potential difference of the pair ofmeasuring terminals is measured, the voltage between both polarities ofeach storage circuit can be measured.

In addition, the terminal voltage detecting section may include aplurality of first switches (62, 64, 66) each having one end connectedto one electrode of the each storage circuits (B1, B2, B3), one of thepair of measuring terminals (both ends of 71) may be connected to a nodethat sets a reference electric potential, and the voltage detectingsection (67 to 69, 71) may include a plurality of second switches (61,63, 65) each connected between the other end of the each first switch(62, 64, 66) and the other electrode of the each storage circuit (B1,B2, B3), a plurality of capacitors (67 to 69), corresponding to therespective storage circuits (B1, B2, B3), each having one electrodeconnected to a node between each the first switch (62, 64, 66) and eachthe second switch (61, 63, 65) and the other electrode connected to theother measuring terminal of the pair of measuring terminals (both endsof 71) in common, a third switch (71) connected between the pair ofmeasuring terminals, and a control section (39) that turns on the fistswitch (62, 64, 66) connected to the selected storage circuit (B1, B2,B3) and the third switch (71) to charge the capacitor (67, 68, 69)corresponding to the selected storage circuit (B1, B2, B3) and turns offthe first switch (62, 64, 66) and the third switch (71) and thereafterturning on the second switch (61, 63, 65) connected to the selectedstorage circuit (B1, B2, B3) at the time of showing the differentialvoltage to the pair of measuring terminals (both ends of 71).

Moreover, the plurality of storage circuits (B1, B2, B3) connected toone another in series may be sequentially scanned to show thedifferential voltage to the pair of measuring terminals (both ends of71) for each storage circuit (B1, B2, B3) in order to measure voltagebetween both polarities of the each storage circuit (B1, B2, B3) fromthe terminal voltage detecting section (62, 64, 66) and the voltagedetecting section (67 to 69, 71).

Furthermore, the each storage circuit may include one or multiplesecondary batteries (B1, B2, B3).

Moreover, the each storage circuit may include one or multiplecapacitors (C1, C2, C3).

Furthermore, a voltage balance method according to a fourth aspect ofthe present invention is a voltage balance method of balancing voltagebetween both polarities of each storage circuit of a plurality ofstorage circuits (B1, B2, B3) connected to one another in series,comprising the steps of connecting a capacitor (37, 38) in parallel to astorage circuit selected from the plurality of storage circuits (B1, B2,B3) connected to one another in series to charge/discharge the capacitor(37, 38) from the selected storage circuit (B1, B2, B3), and connectingthe charged/discharged capacitor (37, 38) in parallel to anotherselected storage circuit (B1, B2, B3) different from the selectedstorage circuit (B1, B2, B3) to charge/discharge the another selectedcapacitor (B1, B2, B3) from the charged/discharged capacitor (37, 38).

Moreover, a voltage detection method according to a fifth aspect of thepresent invention is a voltage detection method of detecting voltagebetween both polarities of each storage circuit of a plurality ofstorage circuits (B1, B2, B3) connected to one another in series,comprising the steps of selecting one storage circuit from the pluralityof storage circuits (B1, B2, B3) to charge a first capacitor (67, 68,69) by voltage of one electrode of the selected storage circuit (B1, B2,B3), connecting the first capacitor (67, 68, 69) and a second capacitor(72) to each other in series to apply voltage of the other electrode ofthe selected storage circuit (B1, B2, B3) to the first capacitor (67,68, 69) and the second capacitor (72) connected to each other in series,and detecting the voltage applied to both ends of the second capacitor(72) as voltage between both polarities of the selected storage circuit(B1, B2, B3).

Furthermore, a voltage detection method according to a sixth aspect ofthe present invention is a voltage detection method of detecting avoltage between both polarities of the respective storage circuits of aplurality of storage circuits (B1, B2, B3) connected to one another inseries, comprising the steps of selecting one storage circuit (B1, B2,B3) from the plurality of storage circuits (B1, B2, B3) connected to oneanother in series to detect voltage of one electrode of the selectedstorage circuit, detecting voltage of the other electrode of theselected storage circuit (B1, B2, B3) to show a differential voltagebetween the voltage of the other electrode and the detected voltage to apair of measuring terminals (both ends of 71) as voltage between bothpolarities of the selected storage circuit (B1, B2, B3), and detectingvoltage between both polarities of each storage circuit (B1, B2, B3) atboth ends of the pair of measuring terminals.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a view illustrating a structure of a voltage balance circuitaccording to a first embodiment of the present invention;

FIG. 2 is a time chart of a control signal that controls the ON/OFF of aswitch;

FIG. 3 is a structural view illustrating a voltage balance circuitaccording to a second embodiment of the present invention;

FIG. 4 is a view illustrating a structure of a voltage balance circuitaccording to a third embodiment of the present invention;

FIG. 5 is a view illustrating a structure of a voltage detection circuitaccording to a fourth embodiment of the present invention;

FIG. 6 is time charts of control signals that control the ON/OFF of avoltage applying switch and a charging switch;

FIG. 7 is a view illustrating a structure of a voltage detection circuitaccording to a fifth embodiment of the present invention;

FIG. 8 is a timing chart for scanning of a voltage detection circuit ofFIG. 7:

FIG. 9 is a circuit diagram of a voltage balance circuit of aconventional secondary battery; and

FIG. 10 is a circuit diagram of a voltage balance circuit of acapacitor.

BEST MODE FOR CARRYING OUT THE INVENTION First Embodiment

FIG. 1 is a view illustrating a structure of a voltage balance circuitaccording to a first embodiment of the present invention.

Three secondary batteries B1, B2, and B3 are storage circuits,respectively, and connected to in series to one another.

A voltage balance circuit 30 includes six switches 31, 32, 33, 34, 35,and 36, two capacitors 37, and 38, and a control section 39. The voltagebalance circuit 30 is a circuit that balances voltages of threesecondary batteries B1, B2 and B3.

The switches 31 to 36 are those that connect the secondary batteries B1,B2, B3 to the capacitors 37 and 38. The switches 31 to 36 are formed ofbipolar transistor, FET (Field Effect Transistor), and the like.

One end of the switch 31 is connected to the positive polarity of thesecondary battery B1. The other end of the switch 31 is connected to oneend of the switch 32 by a connecting node N1. The other end of theswitch 32 is connected to the negative polarity of the secondary batteryB1. One end of the switch 33 is connected to the positive polarity ofthe secondary battery B2. The other end of the switch 33 is connected toone end of the switch 34 by a connecting node N2. The end of the switch34 is connected to the negative polarity of the secondary battery B2.One end of the switch 35 is connected to the positive polarity of thesecondary battery B3. The other end of the switch 35 is connected to oneend of the switch 36 by a connecting node N3. The other end of theswitch 36 is connected to the negative polarity of the secondary batteryB3.

The capacitors 37 and 38 are those that move storage energy of thesecondary batteries B1, B2 and B3. The capacitors 37 and 38 havenecessary capacities for that end.

The capacitor 37 is connected between the connecting node N1 and theconnecting node N2. The capacitor 38 is connected between the connectingnode N2 and the connecting node N3. The switches 31 and 33 are thosethat connect the capacitor 37 to the secondary battery B1 in parallelwhen the secondary battery B1 is selected. The switches 33 and 35 arethose that connect the capacitor 38 to the secondary battery B2 inparallel when the secondary battery B2 is selected.

The switches 32 and 34 are those that connect the capacitor 37 to thesecondary battery B2 in parallel when the secondary battery B2 isselected. The switches 34 and 36 are those that connect the capacitor 38to the secondary battery B3 in parallel when the secondary battery B3 isselected.

The control section 39 is one that controls the ON/OFF of the switches31 to 36. Namely, the control section 39 supplies a control signal S1 tothe switches 31, 33, and 35. The control section 39 supplies a controlsignal S2 to the switches 32, 34, and 36. In the control signals S1 andS2, their signal levels change to a high level (hereinafter referred toas “H”) and a low-level (hereinafter referred to as “L”) alternately asillustrated in FIG. 2.

The switches 31 to 36 turn on, respectively when the control signalwhose signal level is H level is supplied thereto. Namely, the switches31 to 36 turn on. Moreover, the switches 31 to 36 open, respectivelywhen the control signal whose signal is L level is supplied thereto.Namely, the switches 31 to 36 turn off.

The control section 39 is structured to include, for example, a pulsegeneration circuit and a flip-flop circuit. It is noted that the controlsection 39 can be structured by a micro computer including a CPU(Central Processing Unit), a ROM (Read Only Memory), a RAM (RandomAccess Memory), and the like.

An explanation will be next given of an operation of the voltage balancecircuit 30 of FIG. 1.

The control section 39 supplies the control signal as in FIG. 2 to theswitches 31 to 36.

As illustrated in FIG. 2, the signal level of the control signal S1 andthe signal level of the control signal S2 change to H level and L levelalternately.

The switches 31, 33, 35 and the switches 32, 34, 36 turn on/offalternately according to the supplied control signals S1 and S2.

When the control signal S1 becomes “H”, the switches 31, 33, and 35 turnon. The connecting node N1 is connected to the positive polarity of thesecondary battery B1 via the switch 31. The connecting node N2 isconnected to the negative polarity of the secondary battery B1 and thepositive polarity of the secondary battery B2 via the switch 33. Then,the connecting node N3 is connected to the negative polarity of thesecondary battery B2 via the switch 35. Thereby, the capacitor 37 isconnected between the positive polarity and the negative polarity of thesecondary battery B1. Moreover, the capacitor 38 is connected betweenthe positive polarity and the negative polarity of the secondary batteryB2. In other words, the secondary battery B1 and the capacitor 37 areconnected in parallel to each other. Also, the secondary battery B2 andthe capacitor 38 are connected in parallel to each other

When the secondary battery B1 and the capacity 37 are connected inparallel to each other, discharging is performed between the secondarybattery B1 and the capacitor 37 according to the voltage between bothpolarities of the secondary battery B1 and the voltage between both endsof the capacitor 37. In other words, when the voltage between bothpolarities of the secondary battery B1 is higher than the voltagebetween both ends of the capacitor 37, the secondary battery B1 chargesthe capacitor 37 via the switches 31 and 33. At the time of charging,storage energy of the secondary battery B1 moves to the capacitor 37.When the secondary battery B1 charges the capacitor 37, the voltagebetween both ends of the secondary battery B1 reduces. Then, the voltagebetween both polarities of the secondary battery B1 and the voltagebetween both ends of the capacitor 37 are substantially equal to eachother. On the other hand, when the voltage between both polarities ofthe secondary battery B1 is less than the voltage between both ends ofthe capacitor 37, the secondary battery B1 is charged by the capacitor37 via the switches 31 and 33. At the time of charging, storage energyof the capacitor 37 moves to the secondary battery B1. When thesecondary battery B1 is charged, the voltage between both ends of thesecondary battery B1 rises. Then, the voltage between both polarities ofthe secondary battery B1 and the voltage between both ends of thecapacitor 37 are substantially equal to each other.

Moreover, when the voltage between both polarities of the secondarybattery B1 and the voltage between both ends of the capacitor 37 areequal to each other, no current flows into the secondary battery B1 orthe capacitor 37 even if the switches 31 and 33 turn on.

When the secondary battery B2 and the capacitor 38 are arranged inparallel, charging is performed between the secondary battery B2 and thecapacitor 38 in the same manner according to the voltage between bothpolarities of the secondary battery B2 and the voltage between both endsof the capacitor 38. Then, the voltage between both polarities of thesecondary battery B2 and the voltage between both ends of the capacitor38 rises and lowers. Thereby, the voltage between both polarities of thesecondary battery B2 and the voltage between both ends of the capacitor38 become substantially equal to each other.

In addition, internal resistance (impedance) and the like of thecapacitor 37 are extremely small as compared with conventional balanceresistance. Accordingly, energy loss caused by discharging becomesextremely small as compared with the conventional case.

Sequentially, the control signal S1 becomes “L.” Also, the controlsignal S2 becomes “H.”

The switches 31, 33, and 35 turn off according to the signal level ofthe control signal S1. Moreover, the switches 32, 34, and 36 turn onaccording to the signal level of the control signal S2. When theswitches 31 to 36 turn on/off in this way, the connecting node N1 isconnected to the positive polarity of the secondary battery B2 via theswitch 32. The connecting node N2 is connected to the negative polarityof the secondary battery B2 and the positive polarity of the secondarybattery B3 via the switch 34. Then, the connecting node N3 is connectedto the negative polarity of the secondary battery B3 via the switch 36.The capacitor 37 is thereby connected between the positive polarity andthe negative polarity of the secondary battery B2. Moreover, thecapacitor 38 is connected between the positive polarity and the negativepolarity of the secondary battery B3. Namely, the capacitor 37 isconnected to the secondary battery B2 in parallel. Moreover, thecapacitor 38 is connected to the secondary battery B3 in parallel.

When the capacitor 38 is connected to the secondary battery B3 inparallel, discharging is performed between the secondary battery B3 andthe capacitor 38 according to the voltage between both polarities of thesecondary battery B3 and the voltage between both ends of the capacitor38.

The control section 39 repeats such ON/OFF control of the switches 31 to36 to balance voltages among the secondary batteries B1, B2, and B3.

For example, in the case where the voltage between both polarities ofthe secondary battery B1 is higher than the voltage between bothpolarities of each of the secondary batteries B2 and B3, the secondarybattery B1 charges the capacity 37 when the switches 31, 33, and 35 turnon and the switches 32, 34, and 36 turn off. For this reason, thevoltage between both polarities of the secondary battery B1 reduces.Moreover, the voltage between both ends of the capacitor 37 increases.

Next, when the switches 31, 33, and 35 turn off and the switches 32, 34,and 36 turn on, the capacitor 37 charges the secondary battery B2, sothat the voltage between both polarities of the secondary battery B2increases. This reduces a difference between the voltage between bothpolarities of the secondary battery B1 and the voltage between bothpolarities of the secondary battery B2.

Next, when the switches 31, 33, and 35 turn on and the switches 32, 34,and 36 turn off, the secondary battery B2 charges the capacitor 38. Forthis reason, the voltage between both ends of the capacitor 38increases.

Next, when the switches 31, 33, and 35 turn off and the switches 32, 34,and 36 turn on, the capacitor 38 charges the secondary battery B3, sothat the voltage between both polarities of the secondary battery B3increases. This reduces a difference between the voltage between bothpolarities of the secondary battery B2 and the voltage between bothpolarities of the secondary battery B3.

In this way, when ON/OFF operations of the switches 31, 33, 35 and theswitches 32, 34, 36 are repeated, so that storage energy moves to thesecondary batteries B2 and B3 with low voltage from the secondarybattery B1 with high voltage via the capacitors 37 and 38. Then,voltages between polarities of the respective secondary batteries B1,B2, and B3 are balanced.

As mentioned above, in the voltage balance circuit 30 of thisembodiment, the capacitors 37, 38 and the secondary batteries B1 and B2are connected in parallel and charging and discharging are performedtherebetween. Thereafter, the capacitors 37, 38 and the secondarybatteries B2 and B3 are connected in parallel and charging anddischarging are performed therebetween. Accordingly, the voltages of thesecondary batteries B1 to B3 can be balanced without loss.

Second Embodiment

FIG. 3 is a structural view illustrating a voltage balance circuitaccording to a second embodiment of the present invention.

A voltage balance circuit 40 of the second embedment is a circuit thatbalances voltages between both ends of the respective capacitors C1, C2,and C3 where a storage circuit includes capacitors C1, C2, and C3connected to one another in series.

The basic structure of the voltage balance circuit 40 is the same asthat of FIG. 1, and includes six switches 41, 42, 43, 44, 45, and 46,two capacitors 47, and 48, and a control section 39 for controlling theswitches 41 to 46 to be turned on and off.

One end of the switch 41 is connected to one electrode of the capacitorC1. The other end of the switch 41 is connected to one end of the switch42 by the connecting node N1. The other end of the switch 42 isconnected to the other electrode of the capacitor C1. One end of theswitch 43 is connected to one electrode of the capacitor C2. The otherend of the switch 43 is connected to one end of the switch 44 by theconnecting node N2. The other end of the switch 44 is connected to theother electrode of the capacitor C2. One end of the switch 45 isconnected to one electrode of the capacitor C3. The other end of theswitch 45 is connected to one end of the switch 46 by the connectingnode N3. The other end of the switch 46 is connected to the otherelectrode of the capacitor C3.

The capacitor 47 is connected between the connecting node N1 and theconnecting node N2. The capacitor 48 is connected between the connectingnode N2 and the connecting node N3.

An explanation will be next given of an operation of the voltage balancecircuit 40 of FIG. 3.

The control section 39 supplies the control signal S1 to the switches41, 43, and 45 similar to the first embodiment. The control section 39supplies the control signal S2 to the switches 42, 44, and 46.

When the switches 41, 43, and 45 are turned on by the control signal S1and the switches 42, 44, and 46 are turned off by the control signal S2,the connecting node N1 is connected to one electrode of the capacitor C1via the switch 42. The connecting node N2 is connected to the otherelectrode of the capacitor C1 and one electrode of the capacitor C2 viathe switch 43. Then, the connecting node N3 is connected to the otherelectrode of the capacitor C2 via the switch 45. Thereby, the capacitor47 is connected to the capacitor C1 in parallel to each other. Thecapacitor 48 is connected to the capacitor C2 in parallel to each other.

The capacitor C1 and the capacitor 47 are connected in parallel to eachother, and charging and discharging are performed therebetween. Whencharging and discharging are performed, the voltage between both ends ofthe capacitor C1 and the voltage between both ends of the capacitor 47become substantially equal to each other. The capacitor C2 and thecapacitor 48 are connected in parallel to each other, and charging anddischarging are performed therebetween. The voltage between both ends ofthe capacitor C2 and the voltage between both ends of the capacitor 48become substantially equal to each other.

When the switches 41, 43, and 45 are turned off by the control signal S1and the switches 42, 44, and 46 are turned on by the control signal S2,the connecting node N1 is connected to one electrode of the capacitor C2via the switch 43. The connecting node N2 is connected to the otherelectrode of the capacitor C2 and one electrode of the capacitor C3 viathe switch 44. Then, the connecting node N3 is connected to the otherelectrode of the capacitor C3 via the switch 46. Namely, connects thecapacitor 47 is thereby connected to the capacitor C2 in parallel toeach other. The capacitor 48 is connected to the capacitor C3 inparallel to each other.

When the capacitor C2 and the capacitor 47 are connected in parallel toeach other, charging and discharging are performed therebetween. Whenthe capacitor C3 and the capacitor 48 are connected in parallel to eachother, charging and discharging are performed therebetween.

For example, when the voltage between both ends of the capacitor C2 islower than the voltage between both ends of the capacitor 47, energy ofthe capacitor 47 moves to the capacitor C2. The voltage between bothends of the capacitor C2 rises. This balances the voltage between bothends of the capacitor C1 and the voltage between both ends of thecapacitor C2 to each other. In addition, when the voltage between bothends of the capacitor 47 is equal to the voltage between both ends ofthe capacitor C2, movement of energy does not occur. Furthermore, whenthe voltage between both ends of the capacitor C2 is higher than thevoltage between both ends of the capacitor 47, energy moves to thecapacitor 47 from the capacitor C2. Thereby, the voltage between bothends of the capacitor 47 and the voltage between both ends of thecapacitor C2 are substantially equal to each other.

Accordingly, the control section 39 repeats ON/OFF control of theswitches 41 to 46 to substantially balance the voltages between bothends of the respective capacitors C1 and C2.

Similarly, regarding the voltages between both ends of the respectivecapacitor C2 and capacitor C3, the control section 39 repeats ON/OFFcontrol of the switches 41 to 46 to substantially balance the voltagesbetween both ends of the respective capacitors C2 and C3. Namely, thevoltages between both ends of the respective capacitors C1 to C3 arebalanced.

As mentioned above, in the voltage balance circuit 40 of thisembodiment, even when the storage circuit includes the capacitors C1,C2, C3, it is possible to balance the voltages between both ends of therespective capacitors C1 to C3 without loss.

Third Embodiment

FIG. 4 is a view illustrating a structure of a voltage balance circuitaccording to a third embodiment of the present invention.

A voltage balance circuit 50 of this embodiment connects multiplecapacitors to the respective secondary batteries B1 to B3.

The voltage balance circuit 50 includes six switches 51, 52, 53, 54, 55,and 56, which are similar to the switches 31 to 36 of the firstembodiment, capacitors 57, 58, and 59 and a control section 39. Namely,the capacitor 58 is added to the voltage balance circuit 50.

One end of the switch 51 is connected to the positive polarity of thesecondary battery B1. The other end of the switch 51 is connected to oneend of the switch 52 by the connecting node N1. The other end of theswitch 52 is connected to the negative polarity of the secondary batteryB1. One end of the switch 53 is connected to the positive polarity ofthe secondary battery B2. The other end of the switch 53 is connected toone end of the switch 54 by the connecting node N2. The other end of theswitch 54 is connected to the negative polarity of the secondary batteryB2. One end of the switch 55 is connected to the positive polarity ofthe secondary battery B3. The other end of the switch 55 is connected toone end of the switch 56 by the connecting node N3. The other end of theswitch 56 is connected to the negative polarity of the secondary batteryB3.

One electrode of the capacitor 57 is connected to the connecting nodeN1. One electrode of the capacitor 58 is connected to the connectingnode N2. One electrode of the capacitor 59 is connected to theconnecting node N3. The electrodes of the respective capacitors 57, 58,and 59 are connected in common.

An operation of the voltage balance circuit 50 will be next explained.

The control section 39 supplies the control signals S1 and S2, which arethe same as those of the first embodiment, to the switches S1 to 56. Theswitches S1, 53, 55 and the switches 52, 54, and 56 turn on/off,alternately.

When the switches S1, 53, 55 turn on, the connecting node N1 isconnected to the positive polarity of the secondary battery B1 via theswitch S1. The connecting node N2 is connected to the negative polarityof the secondary battery B1 and the positive polarity of the secondarybattery B2 via the switch 53. Then, the connecting node N3 is connectedto the negative polarity of the secondary battery B2 via the switch 55.Thereby, the capacitors 57 and 58 are connected in series between thepositive polarity and negative polarity of the secondary battery B1. Thecapacitors 58 and 59 are connected in series between the positivepolarity and negative polarity of the secondary battery B2. Namely, theseries circuits of the capacitors 57 and 58 are connected to thesecondary battery B in parallel. The series circuits of the capacitors58 and 59 are connected to the secondary battery B2 in parallel.Thereby, the voltages applied to both ends of the respective capacitors57, 58 and 59 become ½ as compared with the case in which no capacitor58 is provided. In other words, one having ½ resisting pressure ascompared with the case in which no capacitor 58 is provided can be usedas capacitors 57 to 59.

The secondary battery B1 and the capacitors 57 and 58 perform chargingand discharging therebetween. By charging and discharging, the voltagebetween the secondary battery B1 and the capacitors 57 and 58 reachesthe voltage of the secondary battery B1 or voltage close thereto. Thesecondary battery B2 and the capacitors 58 and 59 perform charging anddischarging therebetween. By charging and discharging, the voltagebetween the secondary battery B2 and the capacitors 58 and 59 reachesthe voltage of the secondary battery B2 or voltage close thereto.

Sequentially, when the switches 51, 53, and 55 are turned off by thecontrol signal S1 supplied by the control section 39 and the switches52, 54, and 56 are turned on by the control signal S2, the connectingnode N1 is connected to the positive polarity of the secondary batteryB2 via the switch 52. The connecting node N2 is connected to thenegative polarity of the secondary battery B2 and the positive polarityof the secondary battery B3 via the switch 54. Then, the connecting nodeN3 is connected to the negative polarity of the secondary battery B3 viathe switch 56. Thereby, the series circuits of the capacitors 57 and 58are connected between the positive polarity and negative polarity of thesecondary battery B2. The series circuits of the capacitors 58 and 59are connected between the positive polarity and negative polarity of thesecondary battery B3. Namely, the series circuits of the capacitors 57and 58 are connected to the secondary battery B2 in parallel. The seriescircuits of the capacitors 58 and 59 are connected to the secondarybattery B3 in parallel.

Regarding the secondary battery B2 and the capacitors 57 and 58,charging and discharging are performed therebetween. Regarding thesecondary battery B3 and the capacitors 58 and 59, charging anddischarging are performed therebetween.

For example, when the voltage between both polarities of the secondarybattery B1 is higher the voltage between both polarities of each of thesecondary batteries B2 and B3, the series circuits of the capacitors 57and 58 are charged by the secondary battery B1. Next, energy is suppliedto the secondary battery B2 from the series circuits of the capacitors57 and 58. Accordingly, the voltages between both polarities of therespective secondary battery B1 and secondary battery B2 are balanced.When the voltages between both polarities of the respective secondarybattery B2 and secondary battery B3 are different from each other, thevoltages between both polarities of the respective secondary battery B2and secondary battery B3 are balanced by the series circuits of thecapacitors 58 and 59, similarly.

In this way, the switches 51, 53, 55 and the switches 52, 54, and 56turn on/off, alternately to eliminate variations in voltages of thesecondary batteries B1 to B3.

As mentioned above, according to the voltage balance circuit 50 of thisembodiment, the series circuits of the capacitors 57 and 58 areconnected to the secondary battery B1 in parallel and the seriescircuits of the capacitors 58 and 59 are connected to the secondarybattery B2 in parallel to charge and discharge the respective capacitors57 to 59. Thereafter, the series circuits of the capacitors 57 and 58are connected to the secondary battery B2 in parallel and the seriescircuits of the capacitors 58 and 59 are connected to the secondarybattery B3 in parallel to charge and discharge the respective capacitors57 to 59. For this reason, similar to the first embodiment, the voltagesof the secondary batteries B1 to B3 can be balanced without loss.

Moreover, in the voltage balance circuit 50, the capacitor 58 isconnected to the connecting node N2 and the connecting node between thecapacitor 57 and the capacitor 59, so that the series circuits of thecapacitors 58 to 59 are formed according to the ON/OFF of the switches51 to 56. For this reason, one having lower resisting pressure can beused as capacitors 57 to 59.

Fourth Embodiment

FIG. 5 is a view illustrating a structure of a voltage balance circuitaccording to a fourth embodiment of the present invention.

A voltage balance circuit 60 of this embodiment is a circuit thatdetects voltage between both polarities of each of the secondarybatteries B1, B2, and B3 connected in series using the voltage balancecircuit 50 according to the third embodiment.

The voltage balance circuit 60 includes six switches 61, 62, 63, 64, 65,and 66, capacitors 67, 68, and 69 and a control section 39.

One end of the switch 61 is connected to the positive polarity of thesecondary battery B1. The other end of the switch 61 is connected to oneend of the switch 62 by the connecting node N1. The other end of theswitch 62 is connected to the negative polarity of the secondary batteryB1. One end of the switch 63 is connected to the positive polarity ofthe secondary battery B2. The other end of the switch 63 is connected toone end of the switch 64 by the connecting node N2. The other end of theswitch 64 is connected to the negative polarity of the secondary batteryB2. One end of the switch 65 is connected to the positive polarity ofthe secondary battery B3. The other end of the switch 65 is connected toone end of the switch 66 by the connecting node N3. The other end of theswitch 66 is connected to the negative polarity of the secondary batteryB3.

The voltage detection circuit 60 further includes a voltage applicationswitch 70, a charging switch 71, and a capacitor 72. The capacitor 72 isa capacitor that holds voltages between both polarities of therespective secondary batteries B1, B2, and B3. The voltage applicationswitch 70 is used to apply voltage. The charging switch 71 is used toperform charging. The control section 39 supplies control signals S61,S62, S63, S64, S65 and S66 to the switches 61, 62, 63, 64, 65, and 66,respectively. Moreover, the control section 39 supplies control signalsS71 and S70 to the charging switch 71 and the voltage application switch70, respectively.

One end of the voltage application switch 70 is connected to one end ofthe capacitor 72. One end of the charging switch 71 is connected to theother end of the voltage application switch 70. The other end of thecapacitor 72 is connected to the negative polarity of the secondarybattery B3. The other end of the charging switch 71 is connected to theother end of the capacitor 72. The connecting node N4 is a connectingnode between the other end of the voltage application switch 70 and oneend of the charging switch 71. The other ends of the respectivecapacitors 67 to 69 are connected to the connecting node N4 in common.

An operation of the voltage balance circuit 60 will be next explained.

Time charts of the control signals S61 to S66, S70, and S71 that controlON/OFF of the switches 61 to 66, the voltage application switch 70 andthe charging switch 71 are illustrated in FIGS. 6(1) to (8).

When the voltage between the polarities of the secondary battery B3 isdetected, the control section 39 supplies the control signals S71, S70,S66, and S65 to the charging switch 71 and the switch 66 and the voltageapplication switch 70 and the switch 65 as illustrated in FIGS. 6(1) to(4).

As illustrated in FIGS. 6(1) and (3), the control signals S71 and S66become “H” and “L” during a secondary battery B3 measuring period at thesame timing. Moreover, as illustrated in FIGS. 6(2) and (4), the controlsignals S70 and S65 become “L” and “H” at the same timing.

When the control signals S71 and S66 become “H”, the charging switch 71and the switch 66 turn on. The charging switch 71 and the switch 66 turnon, so that both ends of the capacitor 69 are connected to the negativepolarity of the secondary battery B3 via the switch 66. Thereby, voltageVc between both polarities of the capacitor 69 becomes zero.Sequentially, the charging switch 71 and the switch 66 turn off and thevoltage application switch 70 and the switch 65 turn on according to thecontrol signals S70, S71, S66, and S65. Thereby, one electrode of thecapacitor 69 is connected to the positive polarity of the secondarybattery B3 via the switch 65. The other electrode of the capacitor 69 isconnected to one electrode of the capacitor 72 via the voltageapplication switch 70. Accordingly, a difference in voltage betweenvoltage VB3 with the positive polarity of the secondary battery B3 andvoltage Vc between both polarities of the capacitor 69 is applied to oneelectrode of the capacitor 72. Here, since the voltage Vc between bothpolarities of the capacity 69 is zero, voltage between both polaritiesof the secondary battery B3 is applied to the capacitor 72. Thecapacitor 72 is charged based on the applied voltage VB3. Next, theswitches 65 and 70 turn off and the switches 66 and 71 turn on again. Atthis time, when charging to the capacitor 72 is insufficient, thevoltage between both polarities of the capacitor 72 does not reach thevoltage between both polarities of the secondary battery B3.

The control section 39 controls ON/OFF of the charging switch 71 and theswitch 66 and the voltage application switch 70 and the switch 65repeatedly, so that the voltage between both polarities of the capacity72 rises. Then, the voltage between both polarities of the secondarybattery B3 and the voltage between both polarities of the capacity 72becomes equal to each other. The voltage between both polarities of thecapacitor 72 is measured under this state, thereby making it possible tomeasure the voltage between both polarities of the secondary battery B3.

When the voltage between both polarities of the secondary battery B2 isdetected, the control section 39 supplies the control signals S71 andS64 to the charging switch 71 and the switch 64, respectively, duringthe period when the voltage between both polarities of the secondarybattery B2 is measured as illustrated in FIGS. 6(1) and (5). The controlsignals S71 and S64 become “H” and “L” at the same time.

Moreover, the control section 39 supplies the control signals S70 andS63 to the voltage application switch 70 and the switch 63,respectively, during the period when the voltage between both polaritiesof the secondary battery B2 is measured as illustrated in FIGS. 6(2) and(6). The control signals S70 and S63 become “L” and “H” at the sametime.

The charging switch 71 and the switch 64 are turned on by the controlsignals S71 and S64, so that both ends of the capacitor 68 are connectedbetween the positive polarity of the secondary battery B3 and thenegative polarity of the secondary battery B3 via the switches 64 and71. Sequentially, when the charging switch 71 and the switch 64 turn offand the voltage application switch 70 and the switch 63 turn on, oneelectrode of the capacitor 68 is connected to the positive polarity ofthe secondary battery B2 via the switch 63. The other electrode of thecapacitor 68 is connected to one electrode of the capacitor 72 via thevoltage application switch 70. Accordingly, a difference in voltagebetween voltage VB2 with the positive polarity of the secondary batteryB2 and voltage Vc between both polarities of the capacitor 68 is appliedto one electrode of the capacitor 72.

Since the voltage Vc between both polarities of the capacity 68immediately before being connected to the capacitor 72 is voltage VB3with the positive polarity of the secondary battery B3, the voltagebetween both polarities of the secondary battery B2 is applied to thecapacitor 72.

Then, the control section 39 controls ON/OFF of the charging switch 71and the switch 64 and the voltage application switch 70 and the switch63 repeatedly, so that the voltage between both polarities of thesecondary battery B2 and the voltage between both polarities of thecapacity 72 becomes equal to each other. The voltage between bothpolarities of the capacitor 72 is measured under this state, therebymaking it possible to measure the voltage between both polarities of thesecondary battery B2.

The same can be applied to the case where the voltage between bothpolarities of the secondary battery B1 is detected, and the controlsection 39 turn on/off the charging switch 71 and the switch 62 and thevoltage application switch 70 and the switch 61, alternately.

The charging switch 71 and the switch 62 are turned on by the controlsignals S71 and S62, so that both ends of the capacitor 67 are connectedbetween the positive polarity of the secondary battery B2 and thenegative polarity of the secondary battery B3.

Sequentially, when the charging switch 71 and the switch 62 turn off andthe voltage application switch 70 and the switch 61 turn on, oneelectrode of the capacitor 67 is connected to the positive polarity ofthe secondary battery B1 via the switch 61. The other electrode of thecapacitor 67 is connected to one electrode of the capacitor 72 via theswitch 71. Accordingly, a difference in voltage between voltage VB1 withthe positive polarity of the secondary battery B1 and voltage Vc betweenboth polarities of the capacitor 67 is applied to one electrode of thecapacitor 72. Since the voltage Vc between both polarities of thecapacity 67 immediately before being connected to the capacitor 72 isvoltage VB2 with the positive polarity of the secondary battery B2, thevoltage between both polarities of the secondary battery B1 is appliedto the capacitor 72.

Then, the control section 39 controls ON/OFF of the charging switch 71and the switch 62 and the voltage application switch 70 and the switch61 repeatedly, so that the voltage between both polarities of thesecondary battery B1 and the voltage between both polarities of thecapacity 72 becomes equal to each other. The voltage between bothpolarities of the capacitor 72 is measured under this state, therebymaking it possible to measure the voltage between both polarities of thesecondary battery B1.

As mentioned above, in the voltage detection circuit 60 of thisembodiment, the voltages between both polarities of the respectivesecondary batteries B1 to B3 are sequentially applied to the capacitor72 by switching of the switches 61 to 66, the charging switch 71, andthe voltage application switch 70. Accordingly, as compared with thecase in which the voltage measuring circuit is provided for each of thesecondary batteries B1 to B3, the voltages between both polarities ofthe respective secondary batteries B1 to B3 can be measured by thesimple structure. Moreover, since the position where the voltage betweenboth polarities of each of the secondary batteries B1 to B3 is measuredis limited to the both polarities of the capacitor 72, it is possible tomeasure each voltage with high accuracy without causing variations inthe measured value.

Fifth Embodiment

FIG. 7 is a view illustrating a structure of a voltage detection circuitaccording to a fifth embodiment of the present invention, and FIG. 8 isa timing chart for scanning of a voltage detection circuit of FIG. 7.Common reference numerals are added to components common to thecomponents in FIG. 5.

A voltage detection circuit 80 is a circuit that detects voltage betweenboth polarities of each of the secondary batteries B1, B2 and B3connected in series, and includes six switches 61 to 66 connected to thesecondary batteries B1 to B3 similar to the fourth embodiment, threecapacitors 67 to 69 connected to the respective switches 61 to 66similar to the fourth embodiment, and a charging switch 71.

The switches 62, 64, and 66 are those that detect the negative voltagesof the respective secondary batteries B1 to B3. The switches 61, 63, 65,the capacitors 67 to 69, and the charging switch 71 are those thatdetect the positive voltages of the respective secondary batteries B1 toB3.

In the voltage detection circuit 80, at the time of detecting thevoltage between both polarities of the secondary battery B3, the controlsection 39 supplies control signals S71 and S66 of “H” to the chargingswitch 71 and the switch 66, respectively as illustrated in FIG. 8. Thecharging switch 71 and the switch 66 turn on. The charging switch 71 andthe switch 66 turn on, so that both ends of the capacitor 69 areconnected to the negative polarity of the secondary battery B3 via theswitches 66 and 71. The control section 39 turns on the charging switch71 and the switch 66 until the voltage Vc between both polarities of thecapacitor 69 reaches completely zero. Sequentially, when the controlsignals S71 and S66 become “L”, the charging switch 71 and the switch 66turn off. The control section 39 thereafter sets the signal level of thecontrol signal S65 to “H.” The switch 65 turns on. Thereby, oneelectrode of the capacitor 69 is connected to the positive polarity ofthe secondary battery B3 via the switch 65. Since the voltage Vc betweenboth polarities of the capacitor 69 is zero, the electric potential ofthe connecting node N4 becomes the same as the electric potential of thesecondary battery B3. At this time, a potential difference between bothends of the charging switch 71 is measured, thereby making it possibleto measure the voltage between both polarities of the secondary batteryB3.

At the time of detecting the voltage between both polarities of thesecondary battery B2, the control section 39 sets the signal level ofthe control signal S65 to “L.” Sequentially, the control section 39 setsthe signal levels of the control signals S71 and S64 to “H.” Thecharging switch 71 and the switch 64 turn on. The charging switch 71 andthe switch 64 turn on, so that both ends of the capacitor 68 areconnected between the positive polarity and the negative polarity of thesecondary battery B3 via the switches 64 and 71. The control section 39turns on the charging switch 71 and the switch 64 until the voltage Vcbetween both polarities of the capacitor 68 reaches the voltage betweenboth polarities of the secondary battery B3. Sequentially, the controlsection 39 sets the signal levels of the control signals S71 and S64 to“L.” The charging switch 71 and the switch 64 turn off. After that, thecontrol section 39 sets the signal level of the control signal S63 to“H.” The switch 63 turns on. Thereby, one electrode of the capacitor 68is connected to the positive polarity of the secondary battery B2 viathe switch 63. At this time, since the voltage Vc between bothpolarities of the capacitor 68 is voltage VB3 with the positive polarityof the secondary battery B3, voltage between the connecting node N4 andthe negative polarity of the secondary battery B3 becomes a differentialvoltage between an electric potential of the positive polarity of thesecondary battery B2 and an electric potential of the positive polarityof the secondary battery B3. Accordingly, a potential difference betweenboth ends of the charging switch 71 is measured, thereby making itpossible to measure the voltage between both polarities of the secondarybattery B2.

The same can be applied to the case in which the voltage between bothpolarities of the secondary battery B1 is detected. First of all, thecontrol section 39 sets the signal level of the control signal S63 to“L.” Sequentially, the control section 39 sets the signal levels of thecontrol signals S71 and S62 to “H.” The charging switch 71 and theswitch 62 turn on. The charging switch 71 and the switch 62 turn on, sothat both ends of the capacitor 67 are connected between the positivepolarity of the secondary battery B2 and the negative polarity of thesecondary battery B3 via the switches 62 and 71. The voltage Vc betweenboth polarities of the capacitor 67 reaches the voltage between thepositive polarity of the secondary battery B2 and the negative polarityof the secondary battery B3.

Sequentially, the control section 39 sets the signal levels of thecontrol signals S71 and S62 to “L.” The charging switch 71 and theswitch 62 turn off. After that, the control section 39 sets the signallevel of the control signal S61 to “H.” The switch 61 turns on. When theswitch 61 turns on, one electrode of the capacitor 67 is connected tothe positive polarity of the secondary battery B1 via the switch 61. Atthis time, since the voltage Vc between both polarities of the capacitor67 is voltage VB2 with the positive polarity of the secondary batteryB2, voltage between the connecting node N4 and the negative polarity ofthe secondary battery B3 becomes a differential voltage between anelectric potential of the positive polarity of the secondary battery B1and an electric potential of the positive polarity of the secondarybattery B2. Accordingly, a potential difference between both ends of thecharging switch 71 is measured, thereby making it possible to measurethe voltage between both polarities of the secondary battery B1.

As mentioned above, in the voltage detection circuit 80 of thisembodiment, since the voltages between both polarities of the respectivesecondary batteries B1 to B3 can be measured at both ends of thecharging switch 71 by switching of the switches 61 to 66 and thecharging switch 71, the structure becomes simpler than the voltagedetection circuit 60 of the fourth embodiment. Moreover, since theposition where the voltage between both polarities is measured islimited to both ends of the charging switch 71, it is possible tomeasure each voltage with high accuracy without causing variations inthe measured value, similar to the fourth embodiment.

In addition, the present invention is not limited to the above-explainedembodiments and various modifications may be possible.

For example, in the voltage balance circuit 40 of the second embodiment,the capacitors C1 to C3 were used as storage circuits in place of thesecondary batteries B1 to B3. However, in the third to fifthembodiments, the secondary batteries B1 to B3 may be changed to thecapacitors C1 to C3. Moreover, each storage circuit may be a circuitincluding multiple secondary batteries and a circuit having multiplecapacitors.

Furthermore, the number of storage circuits such as secondary batteries,capacitors, and the like is not limited to three, and four or more maybe possible.

This application is based on the Japanese Patent Application No.2001-305426 filed on Oct. 1, 2001, entire content of which is expresslyincorporated by reference herein.

INDUSTRIAL APPLICABILITY

The present invention can be used in the industrial field to which thestorage circuits are used.

1. A voltage balancing circuit that balances voltage between bothpolarities of each storage circuit of a plurality of storage circuits(B1, B2, B3) connected to one another in series, comprising: a capacitor(57, 58, 59); a first connecting section (51, 53, 55) that connects saidcapacitor in parallel to a first storage circuit selected from saidplurality of storage circuits wherein said first storage circuitincludes any two of B1, B2, B3 connected to one another in series tocharge/discharge said capacitor (57, 58, 59) from said first storagecircuit; and a second connecting section (52, 54, 56) that connects saidcharged/discharged capacitor (57, 58, 59) in parallel to a secondstorage circuit wherein said second storage circuit includes any two ofB1, B2, B3, wherein said any two of B1, B2, B3 of said second storagecircuit differs from said any two of B1, B2, B3 of said first storagecircuit to charge/discharge said select second storage circuit from saidcharged/discharged capacitor (57, 58, 59), wherein: said firstconnecting section (51, 53, 55) and said second connecting section (52,54, 56) include a first switch (51, 53, 55) and a second switch (52, 54,56) that are connected to each other in series between one electrode ofsaid first and second storage circuits and an other electrode; and oneend of said capacitor (57, 58, 59) is connected to a connecting nodebetween said first switch (51, 53, 55) and said second switch (52, 54,56) that are connected to each other in series between the one electrodeand the other electrode of said first and second storage circuits, andthe other end of said capacitor (57, 58, 59) is connected in common. 2.The voltage balancing circuit according to claim 1, further comprising acontrol section (39) that repeats processing that connects said selectedfirst storage circuit to said capacitor (57, 58, 59) in parallel andprocessing that connects said capacitor (57, 58, 59) to said secondstorage circuit.
 3. The voltage balancing circuit according to claim 1,wherein each storage circuit of said plurality of storage circuitsconnected to one Another in series includes one or multiple secondarybatteries (any of B1, B2, B3).
 4. The voltage balancing circuitaccording to claim 1, wherein each storage circuit of said plurality ofstorage circuits connected to one another in series includes one ormultiple secondary capacitors (C1, C2, C3).
 5. A voltage balancingmethod that balances voltage between both polarities of each storagecircuit of a plurality of storage circuits (B1, B2, B3) connected to oneanother in series, comprising the steps of: controlling a first switch(51, 53, 55) and a second switch (52, 54, 56) connected in seriesbetween one electrode and an other electrode of each storage circuit ofa plurality of storage circuits (B1, B2, B3) connected to one another inseries to balance voltage; connecting each one end of a plurality ofcapacitors (57, 58, 59), each having one end connected to a connectingnode between the first switch (51, 53, 55) and the second switch (52,54, 56) and the other end connected in common, to one electrode of eachof the plurality of storage circuits (B1, B2, B3) to selectseries-connected storage circuits (B1 and B2 or B2 and B3) from thepolarity of storage circuits (B1, B2, B3) and charge/discharge theplurality of capacitors (57, 58, 59) from the selected storage circuits(B1 and B2 or B2 and B3); connecting each one end of the plurality ofcharged/discharged capacitors (57, 58, 59) to the other electrode ofeach of the plurality of storage circuits (B1, B2, B3) to select anotherseries-connected storage circuits (B2 and B3 or B1 and B2) differentfrom the selected storage circuits (B1 and B2 or B2 and B3) from theplurality of storage circuits (B1, B2, B3) and charge/discharge anotherselected storage circuits (B2 and B3 or B1 and B2) to/from the pluralityof charged/discharged capacitors (57, 58, 59).